While a lack of interest may seem like a relatively broad symptom, it is, in fact, a recognized medical event known as anhedonia.
“Anhedonia is one of the main symptoms of depressive disorders. It is the loss of interest in previously rewarding or enjoyable activities. People suffering from clinical depression lose interest in hobbies, friends, work--even food and sex. It's as if the brain's pleasure circuits shut down or short out--but do they? Some experts define hedonic function as the total amount of pleasure that it's possible to gain from a single activity. Perhaps depression reduces that hedonic capacity,” says Faith Brynie, Ph.D., and contributor to Psychology Today.
Many sufferers of PPD report that they simply “go through the motion,” deriving no pleasure from events and activities that once brought them joy. When this occurs, it can easily further compound the other symptoms of PPD.